I try to wash them at least once a week but sometimes I slack. They never go any longer than 3 weeks without a wash.
Kaige, Raustyk & Indy will sometimes jump up to say hi or sleep on the bed during the day but they don't really sleep with us at night. So the sheets don't really get dirty or hairy.
Mako will sleep with me at night though but she only takes up a small amount of space & always sleeps in the same spot.